Page:The New International Encyclopædia 1st ed. v. 19.djvu/627

* TUNNELS— TYPICAL SECTIONS OF THE NEW YORK SUBWAY H^ffr Proofing = ''■■-j'a-'% ^ ^^ j^ '"-Tie Rods vv * T T ^F «5' 126 6'y » 6'3' 1 / s-0- S'O' £X '"Minimum Depth of Concrete $ ' Half Cross Section. Part Longitudinal Section. mi^m Twin single track cast-iron cylindeps under Harlem River, showing concrete envelope and lining. Rectangular section, flat roof I" beam construction. " 1 " beams are used for roof and sides, steel bulb-angle columns forming the centre supports. Concrete-arch tunnel. Construction used for rock tunnel and also for some open- cut work. Cast-iron tubes under East River. Con- structed in rock by ordinary excavation, In sand and silt by hydraulic shields.
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